A crucial point in ceramic production technology is the development of new methods for producing green compacts. Examples of this are ceramic die-casting, gel-casting or near-net shape technology. All processes require the use of large quantities of organic processing aids, such as binders, lubricants or stabilizers which have to be removed from the green parts before or during the sintering process. This debindering process is, first of all, time and cost intensive, and secondly, it gives rise to environmental stresses because of the decomposition products created, that are in part injurious to health.
Binder systems for ceramic green compacts based on polyacrylates and polymethacrylates are available, and are used, for example, in the capacitor industry. In this connection, usually aqueous dispersions of polyacrylates are used for the very thin capacitor foils (2-20 μm). For layer thicknesses beginning at about 100 μm, aqueous systems are no longer economical, because of the long drying times. To the extent that formulations using acrylate resins are used in this connection, they derive from polyvinylbutyral (PVB) formulations, and one uses correspondingly known dispersing agents such as fish oil or phosphoric acid ester, and solvent mixtures such as ethanol/toluene.
Ceramic, especially piezoceramic components include several, especially many layers (many-layer components or multilayer components), and are usable, for example, as actors (add-on components)in piezostacks, in that by voltage control an inertia-poor mechanical deflection of comparatively high force is achieved, or are usable as a flexural element, in that the voltage control brings about a great deflection of lesser force, or they permit the generation of high electrical voltages or are used in appropriate devices for the detection of mechanical vibrations or the generation of acoustical vibrations.
Technical solutions up to now are predominantly based on ceramic masses of the structural type of perovskite of the general formula ABO3, the piezoelectrical properties coming into effect in the ferroelectric state. Lead zirconate-titanate ceramics Pb(Zr1-xTix)O3 (PZT), modified by certain additives, have proven especially advantageous. Between ceramic layers produced according to typical methods of ceramic foil technology there are noble metal internal electrodes that are applied using silk screen printing. The noble metal electrodes permit thermally eliminating the dispersing agents and binders used, as well as the additional organic additives and also the organic components of the silk screen printing metal paste from the multilayer stacks into the air, using depolymerization and oxidation, so that, subsequently, sintering compacting at ca. 1100 to 1150° C. is made possible without reduction effects, possibly caused by remaining carbon residues, become effective, which would negatively influence the properties of the ceramics as a result of reduction reactions.
German patent document no. 100 62 672 A1 refers to piezoelectric components in monolithic multilayer construction, having a stack of at least two ceramic layers and an electrode layer, situated between two ceramic layers, in which the electrode layer contains copper. Using these copper-containing internal electrodes, a practically complete debindering succeeds before the application of the sintering compacting under inert conditions in that one supplies plenty of steam to the inert atmosphere during debindering, and permits only a certain partial pressure of oxygen that leaves the copper-containing internal electrode undamaged. This creates the supposition that, in the process of the subsequent sintering compacting, piezoactors having optimal property values of the ceramics are obtained, that are not second to, or even surpass a piezoceramic layer of respective composition, separated under analogous conditions from the copper-containing electrode layer or even sintered in air. Polyurethane dispersion is used as binder in German patent document no. 100 62 672 A1.
Formulations for casting slip based on solvent mixtures not having aromatic compounds, such as toluene or xylene and not having chlorinated hydrocarbons such as trichloroethylene are not known up to the present, especially in combination with lead-containing powders (e.g. PZT).